ORGANIC EVOLUTION 



25 



between the hereditary factors present, the causes 

 that led to the development of the more complicated 

 stages in the past (the accumulation of hereditary 

 factors) are different from the causes that, at pres- 



1<"lt«*H^ 



Fig. 9. — Antlers of stag', 

 showing successive additions 

 of brandies in successive 

 years. (After Romanes.) 



ent, bring about a similar sequence as the individual 

 gets older. 



It was early recognized that many embryonic 

 stages could not possibly represent ancestral animals. 

 A young fish with a huge yolk sac attached {fig. 10) 

 could scarcely ever have led a free life as an adult 

 individual. Such stages were interpreted, however, 

 as emhryonic additions to the original ancestral 



